Generally speaking, the invention relates to enciphering and deciphering of digital communication paths in data- and/or telecommunication networks. These paths are set up between network terminals which may be any kind of equipment, application, resource, manager, users, etc., attached to the network in one way or another.
Data- and telecommunication networks are built up from communicating switching equipment as e.g. PABXs and PBXs. The switching equipment manages communication paths through sets of communication channels. These communication channels are the physical information carriers. The information signal or the datastream carried by a channel is enciphered whenever security is required. Enciphered data on a channel requires that cryptographic (crypto) devices which carries out the enciphering and deciphering process, must be attached to the data stream connected to the channel.
Such ciphering/deciphering data- and telecommunication networks are earlier known when security is required, and different solutions have been proposed.
Among the most straightforward solutions a link-to-link crypto equipment should be mentioned first. Here each transmission link has a crypto device, including encryption and decryption devices in each of its ends, which system only protects the transmission links themselves. As a second, rather straightforward solution there should be mentioned an end-to-end crypto equipment where each subscriber involved has a crypto device that can be inserted into the traffic channel after the call has been set up. In the latter case also the switches of the network will be included in the crypto traffic.
These solutions give, however, rather expensive and poorly flexible solutions as the crypto devices have to be constantly assigned to the links or to the subscribers involved.
From Japanese Patent Application No. 85-121742 filed on Jun. 4, 1985, inventor Yasuhiro Watanabe (Early-disclosure No.: 86-278256), there is known a solution where each PABX is provided with special cipher trunks for ciphering and deciphering. The terminal units are connected with the public network through office trunks in the case of ordinary communication and through cipher trunks in the case of ciphered communication.
According to the Japanese specification, ciphered communication can be executed between optional terminal units without installing a ciphering circuit and a deciphering circuit for every terminal unit. The Japanese PABX have a number of office trunks which can be used for secured as well as non-secured transmission. Secure messages are routed through one of a number of cipher trunks before transmitting the data through the public network. A central processing unit of the PABX controls connection of terminal units intended for ciphered communication to the public network through the cipher trunks. In this layout the enciphering/deciphering equipment is part of the PABX.